Abrasive articles and method of making the same



p 1961 R. A. BAUMGARTNER EIAL 2,981,615

ABRASIVE ARTICLES AND METHOD OF MAKING THE SAME Filed Sept. 8, 1959 INVENTORS RICHARD A. BAUMGARTNER HOWARD M. CANFI'E LD HALSEY W. BUELL l M ff d.

ATTORNEY United States Patent Ofi'ice ABRASIVE ARTICLES AND METHOD OF MAKING THE SAME Richard A. Baurngartner, Howard M. Canfield, and Halsey W. Euell, Niagara Falls, N.Y., assignors to The Carborundum Company, Niagara Falls, N.Y., a corporation of Delaware Filed Sept. 8, 19 59 Ser. No. 838,789 25 Claims. (Cl. 51-497) This invention relates to abrasive articles of manufacture. More particularly it concerns composite abrasive articles formed from a plurality of layers of abrasive: coated flexiblefibrous sheet material which are assembled and adhesively combined under pressure to form an integrated abrasive body of the desired size and shape such as grinding wheels and discs, polishing wheels and discs, blocks, sticks and other sundry abrasive shapes.

This application is a continuation-in-part application of our co-pending application, Serial No. 471,344, filed November 26, 1954.

Abrasive articles of the grinding wheel type have been made for many years, and still are made, by the conventional practice of preparing a suitable mixture of abrasive grain and bond, with or without additional fillers, pore formers, or other modifying agents, and forming a moldable mass of the desired molding consistency. The material is placed in a mold and compressed to the desired shape after which the resulting molded body is heated or fired to mature the bond. The matured body is then dressed, if necessary, to final form. Such procedure is subject to many variations with respect to nature and size of'the abrasive granules, kind and amount of bond, and type of fillers or other added ingredients and the like, but it remains today inall its various ramifications as the standard practice for making the bulk of abrasive articles of the bonded type.

Some years ago U.S. Patent No. 2,355,667, issued to Romie L. Melton and Albert L. Ball, offered a different method of making abrasive Wheels and shapes in which the desired article was composed of a plurality of layers of flexible fibrous abrasive-containing sheet material in which the abrasive particles were incorporated into the interior of a continuous web of fibers together with a bond for holding the abrasive grit in place and the resulting abrasive-included fibrous sheet material sized with a combining adhesive, a number of plies of the material assembled in superimposed relation and compressed to form the final abrasive article. Articles made according to the Melton and Ball patent have met With considerable commercial success because of their peculiar characteristic two-fold ability of performing a relatively effective cutting action, and at the same time imparting a certain degree of superior finish to the article being abraded. However, where attempts have been made to us such articles under more severe conditions of grinding, especially Where the thickness of the final abrasive body is relatively small, it has been found necessary to reinforce the abrasive body by the incorporation therein of one or more layers of reinforcing fabric. Such reinforced Wheels are described in Goepfert and Cofran U.S. Patent No. 2,540,112.

There has also been a limit to the amount of abrasive particles which could be satisfactorily incorporated within the body of an abrasive article fabricated from an abrasive-included fibrous Sheet material because of the interference of larger amounts of abrasive grain with the interlocking and felting together of the fibers making up the sheet material. Consequently, there has been a demand for an abrasive article of the general type heretofore provided by the Melton and Ball article but which would have greater bursting strength and would also permit the use of increased amounts of abrasive granules in proportion to fiber andbond so as to provide an article of increased cutting ability without undue sacrifice of strength and other resiliency characteristics shown by articles of that type.

Previous attempts, and there have been many, to make an abrasive Wheel by forming the wheel from a number of layers of conventional paper or textile fabric having a layer of abrasive grain secured to the surface of the paper or fabric have never met with success. The re sulting wheels have either failed to have adequate strength for most grinding purposes or the alternate layers of textile fabric or other means of support for the abrasive grains have resulted in a lack of integration Within the article to the extent that the non-abrasive components of the final shape interfered with the grinding action. Instead of imparting the desired characteristics sought for in such a wheel they introduced irregularities in cutting action to the Wheel so that it became actually inferior to the conventional bonded type of abrasive article Without introducing any compensating desirable features.

It is an object of the present invention to provide new and improved abrasive articles of the fibrous type.

It is a further object to provide fibrous abrasive articles in which full benefit will be derived from the beneficial presence of the fibrous component without the latter detracting unduly from the grinding efficiencies of the article.

Other objects and advantages accruing from the invention will become apparent as the description proceeds.

In accordance with the present invention, improved abrasive articles of the fibrous type are made from plurality of layers of abrasive-coated non-woven fibrous sheet material which are compacted and adhesively combined under pressure to form an integral abrasive body of the desired size and shape. We have discovered, contrary to all previous experience, that superior articles of the bonded fibrous abrasive grinding wheel type can be made by the judicious selection of a suitable fibrous carrier medium for the abrasive particles and the proper pretreatment thereof with materials so as to preserve and enhance the strength of its fibrous structure and the use of a combination of binders which will leave the article with satisfactory cutting properties. The abrasive coated non-woven fibrous sheet material from which the resultant articles are formed is selected and prepared as follows:

The non-woven textile fibrous sheet material which serves as a backing or carrier for the abrasive particles, in order to accomplish the purposes of the present invention and providean article of the desired type, must be relatively uniform and light in weight so that when it is embodied in the final article it will not interfere with the grinding action of the abrasive particles or introduce any irregularities or non-uniformities in the overall cutting performance of the article. At the same time it must be of such fibrous Structure as to permit an intermingling and interassociating of all the components of the final article so that homogeneity of grinding action throughout the body of the final molded shape is obtained. Also, the material must be one having adequate strength 'to preserve its continuity of structure throughout the process of introducing the abrasive particles and various impregnating and bonding ingredients to the sheet material and will retain all or most of its structure and strength-imparting properties in the final product.

Patented Apr. 25 1961 A highly satisfactory type of non-woven textile fibrous sheet or web material for purposes of the present invention-and one which is preferred because of its ease of handling in processing-is a light weight, non-Woven web comprising a blend of cotton fibers and thermoplastic fibers and which. has been heat-calendered to a compact form. For example, a web composed of about 80% cotton fibers and 20% cellulose acetate fibers having a ream weight of around 4% pounds per ream calendered to athickness of .003-.004 with a tensile strength, lengthwise, of 10-12 pounds/inch, has been found very satisfactory. Wherever reference is made herein to a ream itis to be understood as being a sandpaper makers ream which is an area equivalent to the area of 480 sheets 9" x 11" in size.

However, other non-woven fabrics of comparable characteristics can be used. For example, a light weight, nonwoven fibrous sheet material composed of cotton fibers and a powdered cellulose acetate thermoplastic binder calendered to desired thickness in the order of magnitude of .003 to .004 of an inch thickness and having comparable strength characteristics can be used. Otherthermoplastic components in fiber, powdered or solution form, can be used in place of the cellulose acetate fibers or powders, such as other thermoplastic cellulosic esters, or derivatives, thermoplastic vinyl compounds, various thermoplastic resinous materials, or plasticized thermosetting resins and the like. It is usually undesirable, and fully equivalent results are not normally obtained in the absence of a thermoplastic constituent of one form or another because of the processing difficulties involved due to lack of initial strength of such materials. However, 100% cotton, or other non-woven textile fabrics of comparable lightness in weight and structure can be utilized, at least to a limited degree, as the base fabric or supporting carrier for the abrasive particles provided the processes of handling are adjusted to compensate for the low strength inherent in such materials.

Having selected a non-woven fibrous, sheet material, the base sheet material of the selected type in Web form is treated or impregnated with a permanently flexible, resilient or elastomeric material in such an amount that the fibers of the fibrous sheet are encapsulated with a thin protective film of the permanently flexible impregnant without filling the interstitial spaces between the adjoining fibers with the impregnant. In other Words, this impregnant, which may be referred to as a presize, and can be applied as such if desired, should be a material which when exposed to the temperatures necessary for compacting and maturing the final shaped abrasive article will not set to a hard friable condition but will remain in a permanent, relatively flexible resilient state so as to protect the individual fibers of the fibrous Web from any undue embrittlement or loss of strength which might otherwise result by absorption of the harder binders usually used to bond the abrasive particles and/or secure the layers of the abrasive-coated fibrous sheet material together in the final article. This impregnating material therefore acts as a permanent anti-embrittling agent for the fibers of the fibrous structure. Various permanently thermoplastic or elastomeric substances can be used for the impregnating presize such as compounded natural rubber latexes, compounded synthetic rubber latexes, such as the various butadiene rubbers including butadiene-styrene copolymers, butadiene-acrylonitrile copolymers, polychloroprene and other synthetic elastomeric compounds, the aforesaid polymeric materials blended with casein and/or various cellulose derivatives such as methyl cellulose, the various thermoplastic resinous polymers such as the vinyl acetal polymers and permanently plasticized thermosetting resins and the like.

After the non-woven fibrous web of the aforesaid described type has been treated or impregnated and dried to a substantially non-tacky condition, a layer of anchoring adhesive is aplpied to one side of the treated or impregnated sheet material and a layer of abrasive grains of the desired grit size applied to the still tacky, adhesively-coated surface. The amount of anchoring adhesive is carefully controlled so that it will be insufficient in quantity to completely fill the interstices of the fibrous supporting structure and will not penetrate through to the opposite or back side of the web.

An anchoring adhesive which has been found highly satisfactory in making articles of the herein described type is a blend of solubilized casein and neoprene latex in the proportion of to parts by weight of casein and 100 parts by weight of neoprene latex having a solids content of 50% neoprene. However, other anchoring adhesives or binders can be used such as casein, casein and butadiene-styrene, casein and butadiene-acrylonitrile, phenol-butadiene acrylonitrile formulations, polyacrylics and modified acrylics, polystyrenes, vinyls, epoxys and polyesters.

Although not necessarily so, it is preferable for best results that the anchoring adhesive or binder is one such as the above enumerated thermoplastic binder materials which when fully cured or set has a degree of hardness somewhat less than the hardness of the material used for the final top sizing coat of binder.

When the anchoring adhesive is'a permanently thermoplastic or elastomeric material, such as a blend of solubilized casein and neoprene latex, the 'pre-sizing or impregnation of the fibrous sheet material to encapsulate the fibers and protect them against embrittlement can be accomplished simultaneously with the application of the anchoring adhesive by applying a single coating of the adhesive to the fibrous sheet in sufficient amount that a portion of the adhesive penetrates and encapsulates the fibers, leaving the remainder of the adhesive on the one surface of the sheet as a tacky film receptive to the coating of abrasive grains to be applied thereto.

After applying the abrasive grains and drying, the abrasive-coated fibrous web is then given a final sizing coat of bonding adhesive which is applied in suflicient amount to not only permanently bond the abrasive particles to the fibrous backing but also will serve to penetrate the fibrous backing of the adjoining layer during the subsequent combining operation to fill the interstices thereof with the supplemental binder material and provide a means of adhesively combining the material when it is assembled in layers to form an abrasive article.

The abrasive-coated fibrous web material with the final size coating of binder is dried or partially cured to a non-tacky condition suitable for handling.

The final bonding or top sizing adhesive is usually applied by dip-coating and is desirably of a harder, more brittle or friable character than the more elastic, or thermoplastic prior coatings of material. The final adhesive serves to impart suitable strength and breakdown properties to the final abrasive article in the course of its use in grinding operations. It is usually a heat-hardenable composition such as a thermo-setting resin, but can be some other polymeric material having suitable binding properties. For example, casein with its macromolecular structure, having a molecular Weight estimated to be substantially in excess of 12,000, and being suitably adhesive in character will serve as an acceptable binder when heathardened, and for purposes herein is considered as a polymeric substance as the term is herein applied. However, for most purposes, very satisfactory results have been obtained by the use of various phenol-aldehyde condensation product resin compositions, such as those set forth in the specific examples given below. Other suitable resinous binders of polymeric form include urea formaldehyde resins, polyester resins, melamine formaldehyde resins, and epoxy resins.

The abrasive-coated fibrous web material thus produced is cut into blanks of required size and shape which are then assembled and adhesively secured together in superimposed relation and subjected to sufficient heat and pressure to compact the layers and adhesively combine the plies of material to form an integral abrasive shape. During the course of the final compacting operation the adhesive binder which has been applied as a final sizing coat flows into the interstices of the fibrous web and also acts as a combining adhesive. During the plastic flow which takes place in the course of the compacting operation the abrasive particles undergo a lateral displacement throughout the article to the extent that the resulting abrasive body has a substantially uniform abrasive action across the entire cross-section of the article,

In order to better understand the nature of the abrasive articles of the present invention and methods for their manufacture, reference is made to the accompanying drawing, the various figures of which are as follows:

Figure l is a perspective view of an abrasive wheel made in accordance with the present invention;

Figure 2 is an enlarged vertical elevation of the abrasive wheel shown in Figure l and illustrates the general laminated structure of the article;

Figure 3 is a highly enlarged vertical sectional view through a single layer of the abrasive-coated non-woven fibrous sheet material from which an article of the type shown in Figures 1 and 2 is constructed; and

Figure 4 is a grossly exaggerated detail vertical section taken through a fragment of an abrasive wheel of the type shown in Figures 1 and 2.

Referring further to the various figures of the drawing, the abrasive wheel 6 provided with a central mounting arbor 7 is composed of a plurality of layers 8 of abrasivecoated non-woven fibrous sheet material of the hereindescribcd type compacted and adhesively combined to form an integrated, substantially homogeneous abrasive body. Each of the initial individual layers 8 which make up the wheel is composed of a light weight non-woven fibrous support or backing layer 10' and a surface coating of abrasive granules 1 1 adhesively secured thereto by means of an anchoring adhesive 12 and final size coating 13. Referring specifically to Figure 4 which shows diagrammatically in further detail the nature of the integrated abrasive-fibrous structure of the abrasive body after the layers 8 have been comp-acted and heat-set, the abrasive granules 11, anchoring adhesive 12 and size coating 13 have been subjected to a certain amount of lateral displacement and plastic flow during the compacting step so as to impart a relatively uniform cutting behavior to the final body. In other words, the size coating 13 has penetrated the fibrous backing without, however, disrupting the encapsulating envelope 9 of elastomeric material about the individual fibers 14 so that the fibrous structure retains most, if not all, of the original strength of the elasticized fibers and atthe same time has the ability to break down at the proper time in use without smearing or interfering with the cutting action of the abrasive grains 11. It is also noted that the abrasive grains 11 have penetrated into the interstices of the fibrous structure to eliminate, or at least minimize, any stratified action in the overall body of the abrasive article.

The invention is further illustrated by the following specific examples:

EXAMPLE 1 An abrasive-coated, non-woven fibrous sheet material suitable for making abrasive articles of various sizes and shapes in accordance with the present invention is made as follows:

An unbleached, non-woven fibrous sheet stock composed of a blend of cotton fibers and 18-22% of cellulose acetate fibers, having a weight of 4.2 to 4.7 pounds per ream, a lengthwise tensile strength of 12 pounds/inch, and hot-calendered to a thickness of about .003.004 of an inch is used as the raw material. The sheet material of the described type is first dip-sized with a compounded polychloroprene latex. The thusly presized material, after at 275 F. for 15 minutes.

Casein glue 750 Polychloroprene latex -Q. 600 l-Iydroxyethyl cellulose 25 Water 1,600

The making coat of adhesive is applied at the rate of 6.5 pounds per ream wet weight and is applied to the sheet material by roll coating. While the making adhesive is still wet and tacky 40 pounds per ream by weight of 24 grit size fused alumina abrasive grain is applied to the adhesively-coated surface and the abrasive-coated sheet material dried for one hour at to F. The abrasive-coated web is then dip-sized with a size coating of 20 pounds per ream wet of a furfural solution containing 70% phenol formaldehyde resinous condensation product such as that known and sold as Bakelite resin BR-10190 by the Bakelite Division of Union Carbide & Carbon Sales Company, Bloomfield, New Jersey. The sheet material is then rack-dried for 2% hours at F. to set the resin adhesive to a non tacky condition suitable for handling.

The resulting abrasive-coated non-woven fibrous sheet material made as above described constitutes the raw material for making abrasive articles in further accordance with the present invention. The fibrous abrasive Web is cut into blanks of the desired size and shape and these blanks assembled in piles or stacks and secured together by subjecting to suitable heat and pressure for compacting to the desired density. The resulting molded shape, if necessary, is trimmed or dressed to size in accordance with customary dressing procedures.

EXAMPLE II Using the above-described sheet material of Example I, abrasive cutting-off wheels 10" diameter by Vs" thick with 1" arbor were made by compacting 8 plies of the sheet material at 3,000 pounds per square inch pressure Several of the abrasive wheels so made were subjected to grinding tests in which 40 cuts through 4 diameter C4020 cold finished steel rod stock were made in comparison with similar size abrasive wheels made in accordance with the aforementioned Melton at al. Patent No. 2,355,667 using abrasiveincluded fibrous sheet material and it was found that there was less variation in cutting characteristics from Wheel to wheel in the wheels using the material :of Example I above then in the case of the wheels made using the abrasive-included fibrous sheet material of the, aforesaid patent. Moreover, the cutting etficiencies of the two sets of wheels were comparable. Other wheels of the same described type were subjected to breaking speed tests wherein the wheels were speeded to the breaking point with the following results:

It will be noted that thebursting strengths of the wheels made in accordance with the present invention were "7 20% higher than the bursting speed of the wheels made in accordance with prior art practice.

EXAMPLE III Using the material of Example I, abrasive cutting-off wheels 12" in diameter by A" thick with /2" arbor were made in accordance with the technique set forth in Example II and such wheels also subjected to comparative grinding results and found to be comparable to wheels made in accordance with past practice. It is further noted that when subjected to similar breaking speed tests the wheels made in accordance with the present invention had bursting strengths higher than those made in accordance with past practice.

EXAMPLE IV Using the abrasive-coated non-woven fabric of Example I, abrasive cutting-01f wheels 16" in diameter by thick with 1" arbor were made by pressing 12 layers of the abrasive-coated sheet material at 3,000 pounds per square inch pressure and 275 F. Table II below shows the results of bursting strength tests as compared to wheels made with the abrasive-included sheet material in accordance with past practice of US. Patent No. 2,355,667 and it is noted that the average bursting strength of the present wheels were 16% greater than the average busting strength of similar wheels made according to prior art practice.

Table 11 Material Breaking Speed Surface Feet/Minute Abrasive-coated material of Ex. I above. 28,065

d0 29,112 Ave. 28,065.

10. Abrasive-includgd] material of U.S. Pat- 24,295

ent N 0. 2,355, 6 11 0 22 410 1 12 .do 23,762

EXAMPLE V An abrasive-coated, non-woven fibrous sheet material suitable for making abrasive articles of various sizes and shapes in accordance with the present invention can be made by an alternative process in which impregnation of the fibrous sheet material is combined with the application of the anchoring adhesive as follows:

An unbleached, non-woven fibrous sheet stock composed of a blend of cotton fibers and 18-22% of cellulose acetate fibers, having a weight of 4.5-5.0 pounds per ream, a lengthwise tensile strength of 14 pounds per inch, and hot-calendered to a thickness of about .003 to .004 of an inch is used as the raw material.

An adhesive composition suitable for combined use as the impregnating material and as the anchoring adhesive was prepared as follows:

The 10% methyl cellulose solution was prepared by dissolving 10 pounds of technical grade methyl cellulose in 3 gallons of hot water (140 F.) with constant stirring, followed by adding the remaining 7.8 gallons of water, cold, accompanied by stirring until the mixture is smooth. The adhesive composition is prepared by adding the 10% methyl cellulose solution, the polychloroprene latex, and the casein glue, sequentially to the water in the order named, with continuous mixing.

The adhesive composition is applied to the fibrous sheet material at the rate of 15 pounds per ream, wet weight, and is applied to the sheet material by roll-coating. The adhesive penetrates the fibrous sheet material to encapsulate the fibers thereof, but is sufficient in amount to provide a layer of adhesive on the one sur face of the sheet material for attachment of the abrasive particles. While the adhesively coated web is still wet and tacky, 37 pounds per ream by weight of 36 grit size fused alumina abrasive grain is applied to the adhesively coated surface and the abrasive-coated sheet material dried for 1 hour at -100 F. The abrasive-coated web is then dip-sized with a size coating of 12 to 13 pounds per ream, wet, of a phenol-formaldehyde resinous condensation product such as that known and sold as V-1035 resin by the Varcum Chemical Corporation of Niagara Falls, New York. The sheet material is then rack-dried for 4 /z-5 hours at 175v F. to set the resin adhesive to a non-tacky condition suitable for handling.

The resulting abrasive-coated, non-woven fibrous sheet material made as above described can be used as the raw material for making abrasive articles in accordance with the present invention following the same practices outlined above in using the raw material of Example I as herein described. The fibrous abrasive web is cut into blanks of the desired size and shape and these blanks assembled in piles or stacks and secured together by subjecting to suitable heat and pressure for compacting to the desired density. The resulting molded shape, if necessary, is trimmed or dressed to size in accordance with customary dressing procedures.

In practicing the invention any of the abrasive materials in common use may be employed, such as silicon carbide, fused aluminum oxide, fused zirconia, diamonds, boron carbide, flint, corundum, emery, rouge and similar substances. The size of the abrasive particles may vary from the finest polishing or bufiing powders to the coarser grit sizes used in grinding.

We, have found that the character of the abrasive articles produced by the herein described process can be altered to a marked degree by variations in the quantity and character of the adhesive binders employed in the securing of the abrasive particles to the fibrous sheet material and the combining of the fibrous sheets. It is essential, however, in the selection of suitable adhesive binders and sizes for making the coated abrasive sheet material in the aforesaid articles that the associations and combinations of adhesive materials used as the presize or impregnating adhesive, the anchoring binder and as the final top size or coating be in such proportions that the various components when blended in the final cured abrasive article impart acceptable breakdown or friability characteristics, do not smear or otherwise interfere with the cutting action of the abrasive particles, and do not embn'ttle the fibrous structure.

Having described and set forth the invention in detail, the scope of the invention is not to be confined, other than by the appended claims.

We claim:

1. An abrasive article consisting essentially of a plurality of adhesively united layers of abrasive-coated nonwoven textile fibrous sheet material, each of said layers of fibrous sheet material having a ream weight of fibrous material of about 4 pounds per ream and a calendered thickness of the order of magnitude of .003 to .004 of an inch, each of the individual layers of fibrous sheet material being irregularly disposed but retaining the continuity of its original structure, the fibers thereof being encapsulated with a thermoplastic polymeric material that is selected from the group consisting of thermoplastic vinyl polymers, permanently plasticized thermosetting resins, compounded latexes of natural and of synthetic rubbers, blends of such compounded latexes with casein, and blends of such compounded latexes with cellulose derivatives, and that is cured to a permanently flexible and resilient state, the combining bond for the plies of abrasive-coated sheet material comprising a heat-hardened polymer.

2. An abrasive article consisting essentially of a plurality of layers of abrasive-coated non-woven textile fibrous sheet material, each of said layers of fibrous sheet material having a ream weight of fibrous material of about 4 pounds per ream and a calendered thickness of the order of magnitude of .003 to .004 of an inch, each of the individual layers of fibrous sheet material being irregularly disposed but retaining the continuity of its original structure, said fibrous sheet material being impregnated with, and the fibers thereof being substantially encapsulated by, a thermoplastic polymer that is selected from the group consisting of thermoplastic vinyl polymers, permanently plasticized thermosetting resins, compounded latexes of natural and of synthetic rubbers, blends of such compounded. latexes with casein, and blends of such compounded latexes with cellulose derivatives, and that is cured to a permanently flexible and resilient state, the abrasive particles and thelayers of im-t pregnated sheet material being integrally bonded together by a binder comprising a heat-hardenedresin.

3. An abrasive article consisting essentially of a plu rality of layers of abrasive-coated non-woven textile fibrous sheet material, each of said layers of fibrous sheet material having a ream weight of fibrous material of about 4 pounds per ream and a calendered thickness of the order of magnitude of .003 to .004 of an inch, each of the individual layers of fibrous sheet material being irregularly disposed but retaining the continuity of its original structure, the fibrous backing component of said fibrous layers being impregnated with, and the fibers thereof substantially encapsulated by, a permanently thermoplastic polymer that is selected from the group consisting of thermoplastic vinyl polymers, permanently plasticized thermosetting resins, compounded latexes of natural and synthetic rubbers, blends of such compounded latexes with casein and blends of such compounded latexes with cellulose derivatives, the fibrous layers and the abrasive particles thereon being held together by means of a binder comprising a heat-hardened resin.

4. An abrasive article consisting essentially of a plurality of layers of abrasive-coated non-woven textile fibrous sheet material, each of said layers of fibrous sheet material having a ream weight of fibrous material of about 4 pounds per ream and a calendered thickness of the order of magnitude of .003 to .004 of an inch, each of the individual layers of fibrous sheet material being irregularly disposed but retaining the continuity of its original structure, the fibrous backing component of said abrasive-coated sheet material being impregnated with, and the fibers thereof being substantially encapsulated by, a thermoplastic polymer that is selected from the group consisting of thermoplastic vinyl polymers, permanently plasticized thermosetting resins, compounded latexes of natural and of synthetic rubbers, blends of such compounded latexes with casein, and blends of such compounded latexes with cellulose derivatives, said layers being adhesively combined into an integrated abrading bodyby means of a bond comprising a heat-hardened resin.

5. An abrasive article according to claim 4 in which the thermoplastic polymer is a butadiene polymer.

6. An abrasive article according to claim 4 in which the thermoplastic polymer is polychloroprene.

7. An abrasive article according to claim 4 in which the thermoplastic polymer is a thermoplastic vinyl polymer.

8. An abrasive article consisting essentially of a plurality :of layers of abrasivecoated non-woven textile fibrous sheet material adhesively combined by means of a thermoset resin into an integrated abrasive body, each of said layers of sheet material comprising a non-woven fibrous backing impregnated with a thermoplastic polychloroprene compound encapsulating the individual fibers thereof, each of said layers of fibrous sheet material having a ream weight of fibrous material of about 4 pounds per ream and a calendered thickness of the order "of magnitude of .003 to .004 of an inch, each of the individual layers of fibrous sheet material being irregularly disposed but retaining the continuity of its original individual layers, a coating of abrasive grains secured to the fibrous backing by means of an anchoring binder comprising casein and polychloroprene and an added bonding coating comprising a heat-hardened resin polymer.

9. An abrasive article consisting essentially of a plurality of layers of abrasive-coated, non-woven textile fibrous sheet material, each of said layers of fibrous sheet material having a ream weight of fibrous material of about 4 pounds per ream and a calendered thickness of the order of magnitude of .003 to .004 of an inch, each of the individual layers of fibrous sheet material being irregularly disposed but retaining the continuity of its original structure, each of said fibrous layers being impregnated with a permanently thermoplastic polymer encapsulating the individual fibers without filling the interstices between adjoining fibers thereof and that is selected from the group consisting of thermoplastic vinyl polymers, permanently plasticized thermosetting resins, compounded latexes of natural and of synthetic rubbers, blends of such compounded latexes with casein, and blends of such compounded latexes with cellulose derivatives, the granular abrasive coating being secured to said fibrous sheet material and the layers of abrasive-coated fibrous sheet material being adhesively combined by means of a bond comprising a heat-hardened resin, said resinous bond also filling the interstices between the encapsulated fibers of said fibrous sheet material.

10. An abrasive article according to claim 9 in which the thermoplastic polymer is a butadiene polymer.

11. An abrasive article according to claim 9 in which the thermoplastic polymer is polychloroprene.

12. An abrasive article according to claim 9 in which the thermoplastic polymer is a thermoplastic vinyl polymer.

13. An abrasive article consisting essentially of a plurality of layers of abrasive-coated, non-woven textile fibrous sheet material, each of said layers of fibrous sheet material having a ream Weight of fibrous material of about 4 pounds per ream and a calendered thickness of the order of magnitude of .003 to .004 of an inch, each of the individual layers of fibrous sheet material being irregularly disposed but retaining the continuity of its original structure, each of said fibrous layers being impregnated with a permanently thermoplastic polymer encapsulating the individual fibers without filling the interstices between adjoining fibers thereof and selected from the group consisting of thermoplastic vinyl polymers, permanently plasticized thermosetting resins, compounded latexes of natural and of synthetic rubbers, blends of such compounded latexes with casein, and blends of such compounded l-atexes with cellulose derivatives, the granular abrasive coating being secured to said fibrous sheet material and the layers of abrasive-coated fibrous sheet material being adhesively combined by means of a heathardenable binder, said heat-hardenable binder also filling the interstices between the encapsulated fibers of said fibrous sheet material.

14. An abrasive article according to claim 13 in which the non-Woven fibrous backing comprises a blend of apgroximately cotton fibers and 20% cellulose acetate bers.

15. A method of making an abrasive article consisting essentially of a plurality of layers of abrasive-coated, non-woven textile fibrous sheet material which comprises calendering a thin, non-woven textile fibrous sheet material having a ream weight of fibrous material of about four pounds per ream to a calendered thickness of the order of magnitude of .003 to .004 of an inch, impregnating said sheet material with a permanently thermoplastic polymer selected from the group consisting of thermoplastic vinyl polymers, permanently plasticized thermosetting resins, compounded latexes of natural and of synthetic rubbers, blends of such compounded latexes with 1'1 casein, and blends of such compounded latexes with cellulose derivatives, in sufficient amount to encapsulate the fibers thereof without completely filling ,the interstices between the fibers, applying a coating of adhesive to one side of the impregnated and calendered fibrous sheet, applying a coating of abrasive grains to the adhesively coated surface, drying the resulting abrasive-coated sheet material, sizing the abrasive-coated sheet material with a heat-hardenable binder in suflicient amount to fill the interstices between adjacent fibers in the adjoining layer during the subsequent uniting operation and partially curing the resulting sheet material to a substantially nontacky condition, cutting blanks therefrom and assembling a plurality of said blanks in superimposed position and subjecting said assembly to heat and pressure to unite and compact said blanks and form an abrasive article without disrupting the encapsulating envelope of thermoplastic material about the individual fibers.

16. A method of making an abrasive article consisting essentially of a plurality of layers of abrasive-coated, non-woven textile fibrous sheet material which comprises calendering a thin, non-woven textile fibrous sheet material composed of a blend of cotton fibers and thermoplastic fibers to compact said sheet material, impregnating said sheet material with a permanently thermoplastic polymer selected from the group consisting of thermoplastic vinyl polymers, permanently plasticized thermosetting resins, compounded latexes of natural and of synthetic rubbers, blends of such compounded latexes with casein, and blends of such compounded latexes with cellulose derivatives, in sufficient amount to encapsulate the fibers thereof without completely filling the interstices between the fibers, applying a coating of adhesive to one side of the impregnated and calendered fibrous sheet, applying a coating of abrasive grains to the adhesively coated surface, drying the resulting abrasive-coated sheet material, sizing the abrasive coated sheet material with a heat-hardenable binder in sufficient amount to fill the interstices between adjacent fibers in the adjoining layer during the subsequent uniting operation and partially curing the resulting sheet material to a substantially nontacky condition, cutting blanks therefrom and assembling a plurality of said blanks in superimposed position and subjecting to heat and pressure to unite and compact said blanks and form an abrasive article without disrupting the encapsulating envelope of thermoplastic material .about the individual fibers.

17. A method of making an abrasive article consisting essentially of a plurality of layers of abrasive-coated, non-woven textile fibrous sheet material which comprises calendering a thin, non-woven textile fibrous sheet material composed of a blend of cotton fibers and thermoplastic fibers to compact said sheet material, impregnating said sheet material with a rubber latex in sufiicient amount to encapsulate the fibers thereof without completely filling the interstices between the fibers, applying a coating of casein and latex adhesive to one side of the impregnated and calendered fibrous sheet, applying a coating of abrasive grains to the adhesively coated surface, drying the resulting abrasive-coated sheet material, sizing the abrasive-coated sheet material with a heathardenable resinous binder in suflicient amount to fill the interstices between adjacent fibers in the adjoining layer during the subsequent uniting operation and partially curing the resulting sheet material to a substantially nontacky condition, cutting blanks therefrom and assembling a plurality of said blanks in superimposed position and subjecting to heat and pressure to unite and compact said blanks and form an abrasive article without disrupting the encapsulating envelope of rubber latex about the individual fibers.

18. A method of making an abrasive article consisting essentially of a plurality of layers of abrasive-coated, non-woven textile fibrous sheet material which comprises calendering a thin, non-woven textile fibrous sheet material having a ream weight of fibrous material of about four pounds per ream to a calendered thickness of the order of magnitude of .003 to .004 of an inch, applying a permanently thermoplastic polymeric adhesive that is selected from the group consisting of thermoplastic vinyl polymers, permanently plasticized thermosetting resins, compounded latexes of natural and of synthetic rubbers, blends of such compounded latexes with casein, and blends of such compounded latexes with cellulose derivatives, to one side of the fibrous sheet in an amount sufiicient to impregnate the fibrous sheet and encapsulate the fibers thereof without filling the interstices between adjoining fibers and provide a tacky layer of adhesive on one side of the said fibrous sheet, applying a coating of abrasive grains to the adhesivcly coated surface, drying the resulting abrasive-coated sheet material, sizing the abrasive-coated sheet material with a heat-hardenable binder in sufiicient amount to fill the interstices between adjacent fibers in the adjoining layer during the subsequent uniting operation and partially curing the resulting sheet material to a substantially non-tacky condition, cutting blanks therefrom and assembling a plurality of said blanks in superimposed position and subjecting to heat and pressure to unite and compact said blanks and form an abrasive article without disrupting the encapsulating envelope of thermoplastic material about the individual fibers.

19. A method of making an abrasive article according to claim 18 in which the thermoplastic polymeric adhesive is a blend of polychloroprene and casein.

20. A method of making an abrasive article according to claim 18 in which the heat hardenable binder is a resinous phenolic'condensation product.

21. A method of making an abrasive article according to claim 18 in which the thermoplastic polymeric adhesive consists essentially of polychlo-roprene and casein containing a small amount of methyl cellulose.

22. A method of making an abrasive article according to claim 18 in which the thermoplastic polymeric adhesive comprises a blend of polychloroprene and casein and the heat-hardenable binder is a resinous phenolic condensation product.

23. An abrasive article in accordance with claim 2 in which said laminating binder is a heat-hardened phenolic resin.

24. An abrasive article in accordance with claim 4 in which said textile fibrous sheet material comprises a blend of cotton fibers and of thermoplastic fibers.

25. A method in accordance with claim 19 in which said assembly is subjected to a pressure of about 3,000 p.s.i. at 275 F. for 15 minutes.

References Cited in the file of this patent UNITED STATES PATENTS 

1. AN ABRASIVE ARTICLE CONSISTING ESSENTIALLY OF A PLURALITY OF ADHESIVELY UNITED LAYERS OF ABRASIVE-COATED NONWOVEN TEXTILE FIBROUS SHEET MATERIAL, EACH OF SAID LAYERS OF FIBROUS SHEET MATERIAL HAVING A REAM WEIGHT OF FIBROUS MATERIAL OF ABOUT 4 POUNDS PER REAM AND A CALENDERED THICKNESS OF THE ORDER OF MAGNITUDE OF .003 TO .004 OF AN INCH, EACH OF THE INDIVIDUAL LAYERS OF FIBROUS SHEET MATERIAL BEING IRREGULARLY DISPOSED BUT RETAINING THE CONTINUITY OF ITS ORIGINAL STRUCTURE, THE FIBERS THEREOF BEING ENCAPSULATED WITH A THERMOPLASTIC POLYMERIC MATERIAL THAT IS SELECTED FROM THE GROUP CONSISTING OF THERMOPLASTIC VINYL POLYMERS, PERMANENTLY PLASTICIZED THERMOSETTING RESINS, COMPOUNDED LATEXES OF NATURAL AND OF SYNTHETIC RUBBERS, BLENDS OF SUCH COMPOUNDED LATEXES WITH CASEIN, AND BLENDS OF SUCH COMPOUNDED LATEXES WITH CELLULOSE DERIVATIVES, AND THAT IS CURED TO A PERMANENTLY FLEXIBLE AND RESILIENT STATE, THE COMBINING BOND FOR THE PLIES OF ABRASIVE-COATED SHEET MATERIAL COMPRISING A HEAT-HARDENED POLYMER. 